Extracellular signal‐regulated kinases 2 (Erk2) and Erk5 in the central nervous system differentially contribute to central sensitization in male mice

Nervous systems are designed to become extra sensitive to afferent nociceptive stimuli under certain circumstances such as inflammation and nerve injury. How pain hypersensitivity comes about is key issue in the field since it ultimately results in chronic pain. Central sensitization represents enhanced pain sensitivity due to increased neural signaling within the central nervous system (CNS). Particularly, much evidence indicates that underlying mechanism of central sensitization is associated with the change of spinal neurons. Extracellular signal‐regulated kinases have received attention as key molecules in central sensitization. Previously, we revealed the isoform‐specific function of extracellular signal‐regulated kinase 2 (Erk2) in spinal neurons for central sensitization using mice with Cre‐loxP‐mediated deletion of Erk2 in the CNS. Still, how extracellular signal‐regulated kinase 5 (Erk5) in spinal neurons contributes to central sensitization has not been directly tested, nor is the functional relevance of Erk5 and Erk2 known. Here, we show that Erk5 and Erk2 in the CNS play redundant and/or distinct roles in central sensitization, depending on the plasticity context (cell types, pain types, time, etc.). We used male mice with Erk5 deletion specifically in the CNS and found that Erk5 plays important roles in central sensitization in a formalin‐induced inflammatory pain model. Deletion of both Erk2 and Erk5 leads to greater attenuation of central sensitization in this model, compared to deletion of either isoform alone. Conversely, Erk2 but not Erk5 plays important roles in central sensitization in neuropathic pain, a type of chronic pain caused by nerve damage. Our results suggest the elaborate mechanisms of Erk signaling in central sensitization. Using genetic deletion in mice, we demonstrate that extracellular signal‐regulated kinase 5 (Erk5) plays important roles in central sensitization in formalin‐induced inflammatory pain. Extracellular signal‐regulated kinase 2 and Erk5 are involved in discrete but parallel mechanisms underlying central sensitization in the early second phase of formalin‐induced nociceptive behaviors.